SAT Math Multiple Choice Question 469: Answer and Explanation

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Test Information

Question: 469

4.

The graph of the function f(x) = –x 2 – 2x + 8 is shown in the figure above. For what values of x does f(x) = 5?

  • A. –4 and 2
  • B. –3 and 1
  • C. –1 and 9
  • D. 5 and 8

Correct Answer: B

Explanation:

B

Difficulty: Medium

Category: Passport to Advanced Math / Quadratics

Strategic Advice: This question is very straightforward if you understand the language of functions. Although you could set the second equation equal to 0 and solve for x, the solution can be found simply by looking at the graph.

Getting to the Answer: The statement f(x) = 5 means to find the x-values on the graph when y is 5. To do this, draw a horizontal line across the graph at y = 5 and read the x-coordinates of the points where the line intersects the parabola.

The function y = –x2 – 2x + 8 has x-values of –3 and 1 when y = 5.

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